fix(files): file service now sends 304 and 403 headers more reliably

File service now checks if file has been deleted or modified before sending 304 headers.

File service now strips -gzip suffixes from headers to send correct 304 headers for
deflated file types.

Fixes #9571

engine/classes/Elgg/Application/ServeFileHandler.php

@@ -62,12 +62,6 @@ public function getResponse(Request $request) {
 			return $response->setStatusCode(403)->setContent('URL has expired');
 		}
 
-		$etag = '"' . $last_updated . '"';
-		$response->setPublic()->setEtag($etag);
-		if ($response->isNotModified($request)) {
-			return $response;
-		}
-
 		$hmac_data = array(
 			'expires' => (int) $expires,
 			'last_updated' => (int) $last_updated,
@@ -97,6 +91,18 @@ public function getResponse(Request $request) {
 			return $response->setStatusCode(403)->setContent('URL has expired');
 		}
 
+		$if_none_match = $request->headers->get('if_none_match');
+		if (!empty($if_none_match)) {
+			// strip mod_deflate suffixes
+			$request->headers->set('if_none_match', str_replace('-gzip', '', $if_none_match));
+		}
+
+		$etag = '"' . $last_updated . '"';
+		$response->setPublic()->setEtag($etag);
+		if ($response->isNotModified($request)) {
+			return $response;
+		}
+
 		$public = $use_cookie ? false : true;
 		$content_disposition = $disposition == 'i' ? 'inline' : 'attachment';
 
@@ -127,4 +133,5 @@ private function getCookieValue(Request $request) {
 		$session_name = $config['session']['name'];
 		return $request->cookies->get($session_name, '');
 	}
+
 }